/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.beans;

import java.beans.PropertyDescriptor;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.springframework.util.ObjectUtils;
import org.springframework.util.ReflectionUtils;
import org.springframework.util.StringUtils;

/**
 * Helper class for calculating property matches, according to a configurable
 * distance. Provide the list of potential matches and an easy way to generate
 * an error message. Works for both java bean properties and fields.
 *
 * <p>Mainly for use within the framework and in particular the binding facility.
 *
 * @author Alef Arendsen
 * @author Arjen Poutsma
 * @author Juergen Hoeller
 * @author Stephane Nicoll
 * @see #forProperty(String, Class)
 * @see #forField(String, Class)
 * @since 2.0
 */
public abstract class PropertyMatches {

    /**
     * Default maximum property distance: 2
     */
    public static final int DEFAULT_MAX_DISTANCE = 2;


    // Static factory methods

    /**
     * Create PropertyMatches for the given bean property.
     *
     * @param propertyName the name of the property to find possible matches for
     * @param beanClass    the bean class to search for matches
     */
    public static PropertyMatches forProperty(String propertyName, Class<?> beanClass) {
        return forProperty(propertyName, beanClass, DEFAULT_MAX_DISTANCE);
    }

    /**
     * Create PropertyMatches for the given bean property.
     *
     * @param propertyName the name of the property to find possible matches for
     * @param beanClass    the bean class to search for matches
     * @param maxDistance  the maximum property distance allowed for matches
     */
    public static PropertyMatches forProperty(String propertyName, Class<?> beanClass, int maxDistance) {
        return new BeanPropertyMatches(propertyName, beanClass, maxDistance);
    }

    /**
     * Create PropertyMatches for the given field property.
     *
     * @param propertyName the name of the field to find possible matches for
     * @param beanClass    the bean class to search for matches
     */
    public static PropertyMatches forField(String propertyName, Class<?> beanClass) {
        return forField(propertyName, beanClass, DEFAULT_MAX_DISTANCE);
    }

    /**
     * Create PropertyMatches for the given field property.
     *
     * @param propertyName the name of the field to find possible matches for
     * @param beanClass    the bean class to search for matches
     * @param maxDistance  the maximum property distance allowed for matches
     */
    public static PropertyMatches forField(String propertyName, Class<?> beanClass, int maxDistance) {
        return new FieldPropertyMatches(propertyName, beanClass, maxDistance);
    }


    // Instance state

    private final String propertyName;

    private String[] possibleMatches;


    /**
     * Create a new PropertyMatches instance for the given property and possible matches.
     */
    private PropertyMatches(String propertyName, String[] possibleMatches) {
        this.propertyName = propertyName;
        this.possibleMatches = possibleMatches;
    }


    /**
     * Return the name of the requested property.
     */
    public String getPropertyName() {
        return this.propertyName;
    }

    /**
     * Return the calculated possible matches.
     */
    public String[] getPossibleMatches() {
        return this.possibleMatches;
    }

    /**
     * Build an error message for the given invalid property name,
     * indicating the possible property matches.
     */
    public abstract String buildErrorMessage();


    // Implementation support for subclasses

    protected void appendHintMessage(StringBuilder msg) {
        msg.append("Did you mean ");
        for (int i = 0; i < this.possibleMatches.length; i++) {
            msg.append('\'');
            msg.append(this.possibleMatches[i]);
            if (i < this.possibleMatches.length - 2) {
                msg.append("', ");
            } else if (i == this.possibleMatches.length - 2) {
                msg.append("', or ");
            }
        }
        msg.append("'?");
    }

    /**
     * Calculate the distance between the given two Strings
     * according to the Levenshtein algorithm.
     *
     * @param s1 the first String
     * @param s2 the second String
     * @return the distance value
     */
    private static int calculateStringDistance(String s1, String s2) {
        if (s1.isEmpty()) {
            return s2.length();
        }
        if (s2.isEmpty()) {
            return s1.length();
        }
        int d[][] = new int[s1.length() + 1][s2.length() + 1];

        for (int i = 0; i <= s1.length(); i++) {
            d[i][0] = i;
        }
        for (int j = 0; j <= s2.length(); j++) {
            d[0][j] = j;
        }

        for (int i = 1; i <= s1.length(); i++) {
            char s_i = s1.charAt(i - 1);
            for (int j = 1; j <= s2.length(); j++) {
                int cost;
                char t_j = s2.charAt(j - 1);
                if (s_i == t_j) {
                    cost = 0;
                } else {
                    cost = 1;
                }
                d[i][j] = Math.min(Math.min(d[i - 1][j] + 1, d[i][j - 1] + 1),
                        d[i - 1][j - 1] + cost);
            }
        }

        return d[s1.length()][s2.length()];
    }


    // Concrete subclasses

    private static class BeanPropertyMatches extends PropertyMatches {

        public BeanPropertyMatches(String propertyName, Class<?> beanClass, int maxDistance) {
            super(propertyName, calculateMatches(propertyName,
                    BeanUtils.getPropertyDescriptors(beanClass), maxDistance));
        }

        /**
         * Generate possible property alternatives for the given property and
         * class. Internally uses the {@code getStringDistance} method, which
         * in turn uses the Levenshtein algorithm to determine the distance between
         * two Strings.
         *
         * @param propertyDescriptors the JavaBeans property descriptors to search
         * @param maxDistance         the maximum distance to accept
         */
        private static String[] calculateMatches(String propertyName, PropertyDescriptor[] propertyDescriptors, int maxDistance) {
            List<String> candidates = new ArrayList<>();
            for (PropertyDescriptor pd : propertyDescriptors) {
                if (pd.getWriteMethod() != null) {
                    String possibleAlternative = pd.getName();
                    if (calculateStringDistance(propertyName, possibleAlternative) <= maxDistance) {
                        candidates.add(possibleAlternative);
                    }
                }
            }
            Collections.sort(candidates);
            return StringUtils.toStringArray(candidates);
        }


        @Override
        public String buildErrorMessage() {
            String propertyName = getPropertyName();
            String[] possibleMatches = getPossibleMatches();
            StringBuilder msg = new StringBuilder();
            msg.append("Bean property '");
            msg.append(propertyName);
            msg.append("' is not writable or has an invalid setter method. ");

            if (ObjectUtils.isEmpty(possibleMatches)) {
                msg.append("Does the parameter type of the setter match the return type of the getter?");
            } else {
                appendHintMessage(msg);
            }
            return msg.toString();
        }
    }


    private static class FieldPropertyMatches extends PropertyMatches {

        public FieldPropertyMatches(String propertyName, Class<?> beanClass, int maxDistance) {
            super(propertyName, calculateMatches(propertyName, beanClass, maxDistance));
        }

        private static String[] calculateMatches(final String propertyName, Class<?> beanClass, final int maxDistance) {
            final List<String> candidates = new ArrayList<>();
            ReflectionUtils.doWithFields(beanClass, field -> {
                String possibleAlternative = field.getName();
                if (calculateStringDistance(propertyName, possibleAlternative) <= maxDistance) {
                    candidates.add(possibleAlternative);
                }
            });
            Collections.sort(candidates);
            return StringUtils.toStringArray(candidates);
        }

        @Override
        public String buildErrorMessage() {
            String propertyName = getPropertyName();
            String[] possibleMatches = getPossibleMatches();
            StringBuilder msg = new StringBuilder();
            msg.append("Bean property '");
            msg.append(propertyName);
            msg.append("' has no matching field. ");

            if (!ObjectUtils.isEmpty(possibleMatches)) {
                appendHintMessage(msg);
            }
            return msg.toString();
        }
    }

}
